This document is based on Japanese patent application No. 11-293626 filed in the Japanese Patent Office on Oct. 15, 1999, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus and photoconductive belt module having a non-contact proximity charging device. More particularly, the present invention relates to an image forming apparatus and photoconductive belt module having an endless photoconductive belt and a non-contact proximity charging device disposed in close proximity to the endless photoconductive belt.
2. Discussion of the Background
An image forming apparatus having a photoconductive member, such as a laser printer, a photocopier, a facsimile machine or the like generally provided with a charging device for electrically charging the photoconductive member. As an example of charging devices, a contact charging device, such as a contact charging roller, is used. The contact charging device sometimes has a drawback that the device is vulnerable to be soiled by residual toner particles and other residual particles remained on a photoconductive member. The contact charging device also has another drawback that the device sometimes creates a vestige thereof on the photoconductive member while the contact charging device contacts the photoconductive member for a certain period.
In recent years, to improve or solve the above-stated drawbacks, as another type charging device, a non-contact proximity charging device has been suggested and is becoming a focus of attention and going into actual use. The non-contact proximity charging device is disposed in close proximity to the photoconductive member, and therefore is relatively resistant to be soiled, and hardly creates a vestige thereof on the photoconductive member. Lately, such a non-contact proximity charging device is being introduced into full color laser printers and photocopiers.
Meanwhile, full color image forming apparatuses, such as color laser printers and photocopiers may be classified into various types. One type is referred as an intermediate image transfer type, which is provided with a single photoconductive member and an intermediate transfer member. Another type is referred as a tandem type, which is provided with plural, such as three or four, photoconductive members aligned in tandem. Generally, the intermediate image transfer type color image forming apparatus is advantageous for downsizing of the apparatus, and the tandem type color image forming apparatus has an advantage in productivity of forming images.
As photoconductive member used in an intermediate image transfer type image forming apparatus, either one of a photoconductive drum and a photoconductive belt is frequently utilized depending upon design principles thereof, such as a structure of a developing device, a total layout plan of the apparatus or the like. The photoconductive belt is further categorized into a seamless endless photoconductive belt has advantage over a seamless photoconductive belt in costs, and therefore image forming apparatus provided with a seamed endless photoconductive belt are increasing.
When a distance between a photoconductive member and a non-contact proximity charging device is uneven, for example, an unevenness in a longitudinal direction of the charging device, unevenness of electrical charge on the photoconductive member is likely to be generated. Meanwhile, an endless photoconductive belt is liable to flutter; accordingly difficulty has been experienced in maintaining a preferable predetermined distance between the non-contact charging device and a photoconductive belt as compared with a rigid photoconductive drum.
Further, when a seamed endless photoconductive belt is used together with a non-contact proximity charging device, the seam and the proximity thereof are more liable to generate the above-described unevenness of electrical charge because of a step of the seam and thickness unevenness at the seam and the vicinity thereof.
Furthermore, such a step and thickness unevenness at the seam are sometimes liable even to make a contact with the charging device because of vibration of the photoconductive belt caused by the step and thickness unevenness and other reasons. Such a contact causes a short circuit of charging circuitry of the charging deice, a power supply thereof, the photoconductive belt, and others. Such short circuit current is generally very large compared to an ordinary gaseous discharge current between the charging device and the photoconductive belt. Consequently, such large current sometimes damages the charging device and the photoconductive belt.
Further, the short circuit often causes a sharp pulse current, which acts as high frequently spike noises upon a control circuit of the image forming apparatus. Consequently, such spike noises sometimes cause a malfunction of the control circuit of the image forming apparatus.
The present invention has been made in view of the above-discussed and other problems and to address the above-discussed and other problems associated with the background apparatus. Accordingly, an object of the present invention is to provide an image forming apparatus and photoconductive belt module having a non-contact proximity charging device that can improve charge unevenness of an endless photoconductive belt in a stable manner.
Another object of the present invention is to provide an image forming apparatus and photoconductive belt module having a non-contact proximity charging device that can decrease short circuits of a charging circuitry.
These and other objects are achieved according to the present invention by providing a novel image forming apparatus and photoconductive belt module including an endless belt to be electrically charged, a plurality of rollers that span the endless belt around the rollers and rotatively transport the endless belt, and a charging device that electrically charges a surface of the endless belt being disposed opposing one of the plurality of rollers and apart from the surface of the endless belt at a predetermined small distance.